The severity of a stenosis or lesion in a blood vessel may be assessed by obtaining proximal and distal pressure measurements relative to the given stenosis and using those measurements for calculating a value of the Fractional Flow Reserve (FFR). FFR is defined as the ratio of a distal pressure measurement (Pd) taken on the distal side of the stenosis and a proximal pressure measurement taken on the proximal side of the stenosis usually within the aorta (Pa). Conventionally, a sensor placed on the distal portion of a flexible interventional device, such as a guide wire, is utilized to obtain the distal pressure measurement Pd, while an external pressure transducer is fluidly connected via tubing to a guide catheter for obtaining the proximal or aortic pressure measurement Pa. Calculation of the FFR value provides a lesion specific index of functional severity of the stenosis in order to determine whether the blockage limits blood flow within the vessel to an extent that treatment is needed. An optimal or normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and in need of an interventional treatment. Common interventional treatment options include balloon angioplasty and/or stent implantation.
Blood flow through the coronary arteries is affected by fluctuations in the pressure arising proximally of the lesion, e.g., in the aorta, as well as fluctuations in pressure arising distally of the lesion, e.g., in the microcirculation. Accordingly, it is not possible to accurately assess the severity of a coronary lesion by simply measuring the pressure differential across the lesion because the pressure measurement taken on the distal side of the lesion is not purely a residual of the pressure transmitted from the aortic end of the vessel. As a result, for an effective calculation of FFR within the coronary arteries, it is necessary to reduce the vascular resistance within the vessel. Currently, pharmacological hyperemic agents, such as adenosine, are administered to reduce and stabilize the resistance within the coronary arteries. These vasodilator agents reduce the dramatic fluctuation in resistance to obtain a relatively stable and minimal resistance value.
Although various solutions have been proposed to provide the distal pressure measurement Pd for calculating an FFR value, there remains a need in the art for alternative devices and methods for obtaining pressure measurements suitable for use in calculating an FFR value for a given stenosis.